Field
The present disclosure relates to a fuel cell system and a method of controlling of a fuel cell system.
Related Art
A vehicle-mounted fuel cell system disclosed in JP 2015-91207A includes a fuel cell, an FC converter connected with the fuel cell, a secondary battery and a secondary battery converter connected with the secondary battery. Each of the FC converter and the secondary battery converter generally includes a smoothing capacitor. A drive motor for vehicle is connected with high voltage wiring placed between the FC converter and the secondary battery converter. A variety of auxiliary machines are connected with the secondary battery converter.
In the fuel cell system described above, a relay may be provided on a high voltage side of the FC converter to separate the FC converter and the fuel cell from the high voltage wiring. In the state that the fuel cell system of this configuration is at stop, since the electric power charged in the smoothing capacitor for the secondary battery converter is consumed by the auxiliary machines, the voltage of the smoothing capacitor for the secondary battery converter is decreased quickly. In the state that the fuel cell system is at stop, on the other hand, the smoothing capacitor for the FC converter is separated from the drive motor and the auxiliary machines by the relay. The voltage of the smoothing capacitor for the FC converter is thus less likely to decrease, compared with the voltage of the smoothing capacitor for the secondary battery converter. When the fuel cell system is restarted after elapse of only a short time period since a previous stop, the voltage of the smoothing capacitor for the FC converter is likely to be not sufficiently decreased, while the voltage of the smoothing capacitor for the secondary battery converter is sufficiently decreased. In this case, there is a large potential difference between the two smoothing capacitors. Accordingly connecting the relay in this state is likely to generate an excessively high current. This problem arises when a significantly large voltage difference is generated between two smoothing capacitors by any reason.